Zuhal Ozdemir

Seismic amplification at Avcılar, Istanbul

Based on the soil data established previously by a team of researchers at the Technical University of Istanbul, a wave amplification study is conducted for the town of Avcilar, Istanbul, located at about 120 km west of the epicentre of the Kocaeli earthquake of August 17, 1999. It is determined, through the use of well known computer program SHAKE, that the three major predominant periods of the ground are, 1.60, 1.00 and 0.70 s. Thus, the reasons of extensive damage occurred to 5–8 storey high residential buildings in the region, may be attributed to both the long distance effects of the high period waves of the earthquake and soil amplification.

On backward dispersion correction of Hopkinson pressure bar signals

Elastic theory shows that wide spectrum signals in the Hopkinson pressure bar suffer two forms of distortion as they propagate from the loaded bar face. These must be accounted for if accurate determination of the impact load is to be possible. The first form of distortion is the well-known phase velocity dispersion effect. The second form, which can be equally deleterious, is the prediction that at high frequencies, the stress and strain generated in the bar varies with radial position on the cross section, even for a uniformly applied loading. We consider the consequences of these effects on our ability to conduct accurate backward dispersion correction of bar signals, that is, to derive the impact face load from the dispersed signal recorded at some other point on the bar. We conclude that there is an upper limit on the frequency for which the distortion effects can be accurately compensated, and that this can significantly affect the accuracy of experimental results. We propose a combination of experimental studies and detailed numerical modelling of the impact event and wave propagation along the bar to gain better understanding of the frequency content of the impact event, and help assess the accuracy of experimental predictions of impact face load.

Numerical Evaluation of Nonlinear Response of Broad Cylindrical Steel Tanks under Multidimensional Earthquake Motion

In this paper, a fluid-structure interaction (FSI) algorithm of the finite element method (FEM), which can take into account the effects of geometric and material nonlinearities of the tank, buckling of the tank shell, and nonlinear sloshing behavior of the contained liquid, is utilized to evaluate the actual behavior of broad cylindrical steel tanks when subjected to strong earthquake motions. In order to clarify a key question—whether anchoring would prevent earthquake damage to tanks—numerical analyses are carried out on the same tank model having two different support conditions: anchored and unanchored. In addition to two horizontal components of ground motion, the vertical component is also taken into account in order to determine the relative importance of vertical ground motion in the behavior of tanks. The consistency of provisions presented in current design codes and numerical analysis results is evaluated.

A Refined Formula for the Allowable Soil Pressure Using Shear Wave Velocities

Based on a variety of case histories of site investigations, including extensive bore hole data, laboratory testing and geophysical prospecting at more than 550 construction sites, an empirical formulation is proposed for the rapid determination of allowable bearing pressure of shallow foundations in soils and rocks. The proposed expression corroborates consistently with the results of the classical theory and is proven to be rapid, and reliable. Plate load tests have been also carried out at three different sites, in order to further confirm the validity of the proposed method. It consists of only two soil parameters, namely, the in situ measured shear wave velocity and the unit weight. The unit weight may be also determined with sufficient accuracy, by means of other empirical expressions proposed, using P or S — wave velocities. It is indicated that once the shear and P-wave velocities are measured in situ by an appropriate geophysical survey, the allowable bearing pressure as well as the coefficient of subgrade reaction and many other elasticity parameters may be determined rapidly and reliably.

Modelling of Earthquake Hazard and Secondary Effects for Loss Assessment in Marmara (Turkey)

This study proposes an innovative Earthquake Risk Assessment (ERA) framework to calculate seismic hazard maps in regions where limited seismo-tectonic information exists. The tool calculates the seismic hazard using a probabilistic seismic hazard analysis (PSHA) based on a Monte-Carlo approach, which generates synthetic earthquake catalogues by randomizing key hazard parameters in a controlled manner. All the available data was transferred to GIS format and the results are evaluated to obtain a hazard maps that consider site amplification, liquefaction susceptibility and landslide hazard. The effectiveness of the PSHA methodology is demonstrated by carrying out the hazard analysis of Marmara region (Turkey), for which benchmark maps already exist. The results show that the hazard maps for Marmara region compare well with previous PSHA studies and with the National Building Code map. The proposed method is particularly suitable for generating hazard maps in developing countries, where data is not available or easily accessible.

Numerical Simulation of Liquid Sloshing in Tanks

Sloshing waves induced by long-period components of earthquake ground motions may generate high magnitude hydrodynamic forces on liquid storage tanks. Past earthquake experience has shown that the forces generated by the sloshing waves may affect the overall safety of tanks by causing extensive damage on the tank wall and roof. Therefore, the accurate description of these forces is vital for reducing the potential risk of tank failure during an earthquake. Appropriate numerical simulation methods can be used to predict response of liquid storage tanks, as they offer a concise way of accurate consideration of all nonlinearities associated with fluid, tank and soil response in the same model. This chapter is, therefore, devoted to the Finite Element (FE) analysis of the sloshing phenomenon occurring in liquid storage tanks under external excitations. The governing equations for the fluid and structure and their solution methodologies are clarified. Current nonlinear FE modelling strategies for interactions between liquid, tank and soil are presented in great detail. The presented numerical modelling schemes are applied to analyze sloshing response of rectangular and cylindrical tanks when subjected to external excitations. Strong correlation between experimental and numerical results is obtained in terms of sloshing wave height for a rectangular tank model under resonant harmonic motion. Numerical simulations on cylindrical tanks have indicated that tank material, boundary conditions at the base and the presence of a second horizontal component in addition to one horizontal component have negligible effect on the sloshing response of cylindrical tanks when subjected to earthquake motions.

CASE STUDIES A RAPID TECHNIQUE TO DETERMINE ALLOWABLE BEARING PRESSURE

Based on a variety of case histories of site investigations, including extensive bore hole data, laboratory testing and geophysical prospecting, an empirical formulation is proposed for the rapid determination of allowable bearing capacity of shallow foundations. The proposed expression corroborates consistently with the results of the classical theory and is proven to be rapid, reliable and safe. It consists of only two soil parameters, namely, the insitu measured shear wave velocity, and the unit weight. The unit weight may be also determined with sufficient accuracy, by means of another empirical expression, using the Pwave velocity. It is indicated that once the shear and P-wave velocities are measured insitu by an appropriate geophysical survey, the allowable bearing capacity may be determined rapidly and reliably through a single step operation. Such an innovative approach, using the seismic wave velocities only, is considerably cost and time-saving, in practice.